Conversion of lignin to ionic liquids

Abstract

Disclosed herein are lignin-derived ionic liquids and methods for preparing them. The methods include forming a reaction mixture comprising a lignin-derived starting material, a carbonyl compound, and an amine; maintaining the reaction mixture under conditions sufficient to form a lignin-derived aminophenol; and converting the lignin derived aminophenol to the lignin-derived ionic liquid. Monomeric phenols, oligomeric phenols, and polymeric phenols can be used as lignin-derived starting materials.

What is claimed is: 
     
       1. An ionic liquid comprising at least one compound according to Formula I: 
       
         
           
           
               
               
           
         
         wherein: 
         R 2a  is selected from the group consisting of C 1-12  alkyl, C 2-12  alkenyl, C 2-12  alkynyl, C 3-12  cycloalkyl, and C 6-14  aryl; 
         R 2b  is selected from the group consisting of C 1-12  alkyl, C 2-12  alkenyl, C 2-12  alkynyl, C 3-12  cycloalkyl, C 6-14  aryl, and hydrogen; 
         R 3a  and R 3b  are independently selected from the group consisting of hydrogen, C 1-12  alkyl, C 2-12  alkenyl, C 2-12  alkynyl, C 3-12  cycloalkyl, and C 6-14  aryl; 
         R 4  is a polymeric lignin residue; and 
         X is an anion. 
       
     
     
       2. The ionic liquid of  claim 1 , wherein R 2a  and R 2b  are independently selected C 1-6  alkyl. 
     
     
       3. The ionic liquid of  claim 1 , wherein R 3a  and R 3b  are hydrogen. 
     
     
       4. The ionic liquid of  claim 1 , wherein X is selected from the group consisting of fluoride, chloride, bromide, a phosphate, a sulfate, a carboxylate, a fluorophosphate, and a fluoroborate. 
     
     
       5. The ionic liquid of  claim 1 , comprising two or more different compounds according to Formula I. 
     
     
       6. A method for preparing a lignin-derived ionic liquid according to Formula I, 
       
         
           
           
               
               
           
         
         the method comprising: 
         forming a reaction mixture comprising a lignin-derive d starting material, a carbonyl compound, and an amine; 
         maintaining the reaction mixture under conditions sufficient to form a lignin-derived aminophenol; and 
         converting the lignin-derived aminophenol to the lignin-derived ionic liquid; wherein: 
       
       R 2a  is selected from the group consisting of C 1-12  alkyl, C 2-12  alkenyl, C 2-12  alkynyl, C 3-12  cycloalkyl, and C 6-14  aryl; 
       R 2b  is selected from the group consisting of C 1-12  alkyl, C 2-12  alkenyl, C 2-12  alkynyl, C 3-12  cycloalkyl, C 6-14  aryl, and hydrogen; 
       R 3a  and R 3b are independently selected from the group consisting of hydrogen, C 1-12  alkyl, C 2-12  alkenyl, C 2-12  alkynyl, C 3-12  cycloalkyl, and C 6-14  aryl; 
       R 4  is a polymeric lignin residue; and
 X is an anion. 
 
     
     
       7. The method of  claim 6 , wherein the carbonyl compound is selected from the group consisting of a ketone and an aldehyde. 
     
     
       8. The method of  claim 6 , wherein the amine is a primary amine or a secondary amine. 
     
     
       9. The method of  claim 6 , wherein the reaction mixture further comprises a solvent. 
     
     
       10. The method of  claim 9 , wherein the solvent is water. 
     
     
       11. The method of  claim 6 , wherein the reaction mixture consists of the lignin-derived starting material, the carbonyl compound, and the amine. 
     
     
       12. The method of  claim 6 , wherein the reaction mixture is maintained at a temperature ranging from about 25° C. to about 250° C. for a period of time ranging from about 5 minutes to about 24 hours. 
     
     
       13. The method of  claim 6 , wherein converting the lignin-derived aminophenol to the ionic liquid comprises contacting the lignin-derived aminophenol with an acid. 
     
     
       14. The method of  claim 13 , wherein the acid is hydrochloric acid, sulfuric acid, or a combination thereof. 
     
     
       15. The method of  claim 6 , further comprising isolating at least a portion of the ionic liquid.